While most patients have typical SCID with a near complete loss of T cells, ∼1 out of every 4 SCID patients have “leaky” or atypical SCID due to hypomorphic variants in SCID-associated genes, with RAG1, ADA, and RMRP accounting for 57% of these cases (10). The gene discussed is RAG1; the disease is severe combined immunodeficiency.